1. Field of the Invention
The present invention relates to a sensorless motor drive apparatus and a method for protecting and controlling the same, and more particularly to a sensorless motor drive apparatus including a position estimation error detector so that it can determine whether an unexpected error occurs in estimating a position of a rotor of a motor with the sensorless method using a software method, and a method for protecting and controlling the sensorless motor drive apparatus.
2. Description of the Related Art
A conventional sensorless motor drive apparatus will hereinafter be described with reference to FIG. 1.
FIG. 1 is a block diagram illustrating the conventional sensorless motor drive apparatus. Referring to FIG. 1, the conventional sensorless motor drive apparatus includes a rectifier 2 for rectifying an AC voltage generated from an AC power source 1 to a DC voltage; a DC link 3 including a plurality of capacitors, for smoothing the DC voltage, and outputting the smoothed DC voltage to an external part; an inverter 4 for receiving the rectified voltage, and converting the received rectified voltage into a three-phase AC voltage; a current detector 5 for detecting a current transmitted from the inverter 4 from a motor 7; and a controller 6 for estimating a rotation speed and a rotor position of the motor 7 on the basis of voltage and current signals applied to the motor 7, and transmitting a control signal to the inverter 4 to control the motor 7.
The above-mentioned sensorless motor drive apparatus mounts the motor to a specific structure such as a compressor incapable of mounting a sensor therein, and detects the rotation speed and the rotor position of the motor, etc.
If the sensor is mounted to the motor drive apapratus, there arise a variety of problems, for example, the increase of production costs and the reliability deterioration caused by a damaged sensor, etc. The sensorless motor drive apparatus is able to improve the above-mentioned problems.
Operations of the above-mentioned conventional sensorless motor drive apparatus will hereinafter be described with reference to FIG. 1.
The AC voltage generated from the AC power source 1 is applied to the sensorless motor drive apparatus to operate the motor 7. The rectifier 2 rectifies the AC voltage to a DC voltage, and transmits the DC voltage to the DC link 3.
The DC link 3 smoothes the DC voltage received from the rectifier 2, outputs the smoothed DC voltage to an external part. The inverter 4 receives the smoothed DC voltage from the DC link 3, converts the received DC voltage into a three-phase voltage, and outputs the three-phase voltage to the motor 7, so that it properly controls the motor 7.
The sensorless motor drive apparatus further includes the current detector 5, so that the current detector 5 detects the magnitude of a current applied from the inverter 4 to the motor 7. In order to normally operate the motor 7, the controller 6 estimates a rotation speed and a rotor position of the motor 7 using the voltage measured by the DC link 3 and the magnitude of the current detected by the current detector 5, and transmits a control signal capable of controlling the motor 7 in response to the estimated rotation speed and the estimated rotor position of the motor 7 to the inverter 4.
A sensorless control method for the motor 7 is of importance to a guarantee of stability. Typically, if an overvoltage occurs in the DC link 3 contained in the sensorless motor drive apparatus, or if the overcurrent is applied to the motor 7, the motor 7 may be erroneously operated or be damaged, and a compressor to which the motor 7 is mounted may also be damaged, so that the sensorless motor drive apparatus further includes a protective device for guaranteeing the stability to prevent the above-mentioned problems from being generated, for example, an overvoltage detector (not shown), a low-voltage detector (not shown), or an overcurrent detector (not shown).
Each of the overvoltage detector and the low-voltage detector acting as the above-mentioned protective devices receives a voltage signal applied to the DC link 3, and outputs an error signal to the controller 6 when an unexpected error occurs in the received voltage signal. The overcurrent detector receives a current signal from the current detector 5, and outputs an error signal to the controller 6 when an unexpected error occurs in the received current signal.
The controller 6 having received the error signal stops generation of a Pulse Width Modulation (PWM) signal transmitted to the inverter 4 capable of controlling the motor 7, so that the inverter 4 stops operations of the motor 7.
However, in the conventional sensorless motor drive apparatus capable of implementing a sensorless control process by estimating the rotation speed and the rotor position of the motor, if an unexpected error occurs in the sensorless control process, the conventional sensorless motor drive apparatus has no device for detecting the error and coping with the detected error, with the exception of the above-mentioned protective devices, so that there is difficulty in guaranteeing the stability of the sensorless motor drive apparatus.
In more detail, an unexpected error may occur in estimating a rotor position of the motor, and this error is called a position estimation error. However, the position estimation error is not detected by the overvoltage detector, the low-voltage detector, or the overcurrent detector.
Therefore, provided that the motor is continuously operated on the condition that the position estimation error is excessively generated, a normal sensorless control process is not performed, so that the motor drive apparatus and the compressor including the motor are damaged.